Vibro-acoustic modelling of the outer and middle ear using the finite-element method

In this study, a computer-based method called finite-element analysis is us ed to predict the forced-frequency response of the ear, with and without an ossicular replacement prosthesis (PORP 0362, Xomed Surgical Products). The method allows visualisation of the dynamical behaviour of the tympanic mem brane (TM) and of the ossicles. The finite-element model is fully three-dim ensional and includes both ligaments and muscles, and accounts for damping caused by the TM, ligaments, incudostapedial joint and the fluids of the in ner ear. For validation, comparison is made with experimental measurements of umbo displacement taken from the literature. The translation and rotatio n (both anterior-posterior and inferior-superior) of the stapedial footplat e are investigated. It is predicted that the translatory motion of the foot plate decreases with increasing frequency, except when the frequency bf the acoustic signal matches the natura I frequencies of the ossicular chain or outer ear canal. The tilting motion of the stapedial footplate is also pre dicted to depend on frequency of excitation. The presence of a prosthesis c hanges the dynamical response considerably by shifting the natural frequenc ies of the ossicular chain. Ratios of stapes motion with and without the pr ostheses are plotted as a function of frequency allowing this effect to be clearly observed.